Deterioration and damage to concrete can be diagnosed by analyzing light that has been reflected from the concrete after near infrared light is emitted onto the concrete. One such technique is disclosed in, for example, Japanese Unexamined Patent Application Laid-Open No. 2000-14779. This technique can be applied to buildings and structures that are made of concrete, such as a tunnel having an inner wall, a bridge having a concrete portion, and one having a concrete wall.
This technique uses a light source that satisfies the following requirements.    (1) Near infrared light having a wavelength of approximately 0.9 to 2.5 μm can be emitted.    (2) Light amount necessary to diagnose even when a distance from the light source to a measurement point is approximately 10 meters, can be obtained.    (3) Characteristics are stable to temperature variation and other external factors because the light source is basically used outdoors.The light source that satisfies these requirements may be a halogen lamp or a halogen heater.
Moreover, a simply constructed optical system using no special components is necessary in view of outdoor use and cost. Furthermore, this technique involves spectroscopic measurement to conduct diagnosis, and therefore, high wavelength resolution is required to increase the precision of the diagnosis.